Process for making paper pulp



Patented Nov. 10, 1925.

UNITED STATES PATENT OFFICE.

BERTRAM '1. MOBAIN, JOHN E. ALEXANDER, AND GOSTA GENBEBG, OF PORT ED- WABDS, WISCONSIN, ASSIGNORS T0 NEKOOSA-EDWARDS PAPER COMPANY, 01 PORT EDWARDS, WISCONSIN, A CORPORATION OF WISCONSIN.

rnocnssroa MAKING PAPER PULP.

No Drawing.

To all whom it may concern:

Be it known that we, BERTRAM T. MCBAIN and JOHN E. ALEXANDER, citizens of the United States, and GOSTA GENBERG, a' sub-. ject of the King of Sweden (who has declared his intention of becoming a citizen of the United States), all of whom are residents of Port Edwards, in the county of Wood and State of Wisconsin, have invented certain new and useful Improvements in a Process for Making Paper Pulp; and we do hereby declare that the following is a full, clear, and exact description of the same.

This invention relates to the production of wood pulp such as is used for making white paper from wood. The invention relates more particularly to the treatment of coniferous wood or other woods that are rich in rosinor similar substances which ordinarily produce dark colored pulp. Because of the continually increasing scarcity of such woods as. spruce that lend themselves to the manufacture of bleached sulphite pulp, it is desirable to find a way to make white paper from woods like southern pine that must be treated by the sulphate process. Woods of this kind, however, yield a dark colored pulp which even after excessive bleaching remains of an undesirable color. Moreover, suchexcessive bleaching makes a ver weak paper. The pulp made by the sulp ite process is easily bleached but makes paper of less strength. It is an object of the present invention tosecure the easy bleaching quality of sulphite pulp and the strength of paper from sulphate pulp.

It is a further object of this invention to provide a method by which wood that requires the sulphate treatment may be made to produce paper which will be nearly white without the use of enough bleaching to materially impair the strength of the-paper.

It is a further object of this invention to produce white paper from kraft pulp.

It is a further object of this invention to make use of the bleaching action of sulphite acid for the treatment of pulp which has been prepared by a sulphate process.

It is a further object of this invention to produce a method wherebg paper,.having the strength of brown kra pa er and the color of paper made by the sulp its process Application filed September 2, 1922. Serial No. 586,037.

from deciduous wood, may be produced from coniferous wood.

It is a further object of this invention to produce a paper by the sul hite process without the necesssity of carefhlly separating all knots, bark or partially decayed wood as has heretofore been necessary when preparing white paper by said process.

- Other and further important objects of the invention will be apparent from the disclosure in the following description, which sets forth the preferred form of our invention.

In making pulp according to our invention, the wood is first cut to appropriate sized chips by. machines such as are already familiar to workers in this art. It is not necessary, however, to separate the bark, knots, partly decayed woodor other sources of dark color with the care which would be needed if the ordinary sulphite process were used. It is sufiicient to make such separation as is usually required for the production of dark brown or kraft pulp by the sulphate process.

The chips thus prepared are cooked according to the usual sulphate process, the sulphate liquor being made up by the use of water and white liquor principally, as little black liquor as possible being employed. The

sulphate pulp may be transferred directly from the sulphate cooker to a sulphite cook-- er, and washed; therein, or the sulphate pulp may be first subjected to washing and lapping and the sheets may then be shredded and the shredded pulp introduced into the sulphite cooker. If desired, instead of sulphate pulp prepared in the way just de-' scribed, ordinary commercial sulphate pulp may be employed.

When the sulphate pulp has been put in the sulphite digester, sulphite. acid is used. Preferably this acid should have a proximately 4% for its total SO, content of which about one uarter is in combined form as sulphite o calcium, and suflicient acid should be added to the pulp to make the contents of the digester have about the density corresponding to 10% of pulp. A higher density is to be avoided, because good circulation cannot be secured with it. The con should be gradually raised to a maximum of 300 F. The pressure should rise rapidly to about 70 pounds,- this point being reached as soon as possible, instead of a lower pressure being maintained during the first twothirds of the cooking time as is the practicein treating chips. The pressure should not there drained and washed in the usual mantemperature.

ner. The recovered liquor maybe used over again by being mixed with the sulphite acid. After the pulp has been sufliciently washed, it is made into sheets by being passed over lapping machines in the usual way.

Bleaching powder or other bleaching agent may be added either in the'blow tank or during the lapping or at a later stage as desired. While the pulp is being bleached,

care shouldbe taken to avoid too high a The bleaching temperature ought not at any time to exceed 95 F. This is tomake sure that no waste of chlorine, through the formation of chlorate, occurs.

The pulp made by this process may be used upon a paper. machine and produces a sheet of paper sufliciently light colored for use as news printing or even as writing paper. The sulphite acid acts not only to directly lighten the color of the paper by its action upon the lignine and other darkening substances but also by so changing some of these substances that they are more easily bleached by the chlorine or other bleaching agent used in the after treatment.

It is to be understood that although we have described the treatment of the sulphate pulp by cooking-in a sulphite digester, the bleaching results obtained by the use of sulphite acid may be obtained by mixing sulphite acid with the pulp in the blow tank or by sprinkling sulphite acid on the pulp on the wet machine, or by applying sulphite acidto the pulp in any other desired way. It is further to be understood that numerous details of the process may be varied through a wide range without departing from the spirit of this invention, and we do not desire limiting the patent granted otherwise than is necessitated by the prior art.

We claim as our invention:

1. The process of making a light colored paper from resinous wood, which comprises treating the wood by the usual sulphate process and then treating the resulting pulp with sulphite acid. I

2. The process of making paper pulp which comprises treating resinous wood with an alkali sulphate solution and then .treating the resulting pulp with an acid solution containing S0 3. The process of making a strong white paper from 'kraft pulp, which comprises treating the pulp with a liquor of acid calcium and magnesium sulphite, and acting upon the result with a bleaching agent.

1. The process of making white pulp.

from sulphate pulp which comprises cooking the sulphate pulp in a digester with sulphite acid at a pressure between and 80 pounds and at a temperature above the boiling point of water for a period exceeding two hours.

5. The process of making white pulp from sulphate pulp-which comprises cooking the sulphate pulp in a digester with sulphite acid at a pressure between 50 and 80 pounds and at a temperature above the boiling point of water for a period exceeding two hours, separating the resulting pulp from the sulphite liquor, and washing and bleaching the pulp.

6. The process of making a light colored paper from dark sulphate pulp which consists in treating the sulphate pulp in a digester with sulphite acid.

7. The process of making a light colored paper from dark sulphate pulp which consists in treating the sulphate pulp in a tank with sulphite acid.

In testimony whereof we have hereunto subscribed our names.

BERTRAM T. MGBAIN. JOHN E. ALEXANDER. GOS TA GENBERG. 

